High performance loudspeakers employ what is often referred to as a "force over area" concept to reduce the unwanted structural vibrations encountered in the older and more popular dynamic cone speakers. Such force over area loudspeakers which use metallic ribbon elements positioned in a magnetic field or plastic diaphragms positioned in an electric field are well known to those in the art and have been demonstrated to have advantages compared to cone speakers.
Ribbon and electro-static loudspeakers, however, although minimizing the level of unwanted, structural vibrations evident in cone speakers, still produce some undesirable structural vibrations and acoustical diffraction effects which are caused by the manner in which the magnetic or electric fields are mechanically implemented and the mechanization of the ribbon or electric drive diaphragm.
An example of a speaker configuration using ribbon elements is described in U.S. Pat. No. 4,550,228, issued on Oct. 29, 1985 to Walker et al. The system disclosed therein comprises high frequency (tweeter), mid-range frequency, and low frequency (woofer) ribbon transducer units. While the structure thereof performs reasonably well, the ribbon structures and magnetic field implementations thereof utilize mechanical elements and relatively sharp diffracting surfaces between the acoustical ribbon transducer driver elements and the listener which physically interfere with the desired acoustic signal output therefrom. Such implementations cause an undesirable coloration or distortion of the acoustical output, i.e., the acoustical output signal includes undesirable signal components due to non-linearities, undesired resonances or other frequency dependent effects, mechanical compression effects, noise, and the like. In addition, the ribbon transducer elements themselves exhibit adverse structural effects associated with various different structural design approaches used in such speakers. Examples of such approaches include the use of a simple corrugated thin metallic ribbon used with an array of damped suspension supports on the edges of the ribbon, the use of a corrugated plastic/metallic laminated ribbon used with an integral plastic suspension array brought out to the edges thereof, the use of a foam suspension array for ribbon support, and the use of a laminated ribbon used with a group of spaced rectangular conductors for impedance matching. Such structures have been found to add unwanted distortion to the acoustical output which it is desired to minimize, or eliminate, if possible.
Accordingly, it is an object of the present invention to provide an improved loudspeaker system which provides an accurate high resolution reproduction of sound over the full acoustic range thereof with a reduced level of coloration or distortion.
It is yet another object of the invention to produce a improved ribbon speaker system having reduced ribbon structural resonances and distortions typically found in prior art cone or electric and magnetic planar field speakers.
It is yet another object of the invention to produce an improved ribbon speaker system having reduced physical interferences with the acoustical output signal and having reduced diffraction effects arising from any baffling and/or the return magnetic circuit path structures used in the system.